1. Field of the Invention
The present invention relates to a hermetic motor compressor for use in an air-conditioning appliance, refrigeration equipment, and the like, and relates further to a method of assembling the same.
2. Description of the Related Art
A hermetic motor compressor of the prior art and a method of assembling it will be described hereinafter with reference to FIG. 5.
In FIG. 5, a body shell 1, an upper shell 5, and a bottom shell 7 constitute a hermetically sealed enclosure. A compression mechanism 300 is disposed in an upper part of the hermetically sealed enclosure. A main shaft 34 constructed at an end of a crankshaft 33, which rotatory drives a orbiting scroll member 32, is journally supported by a main bearing 35, as it extends downward. A motor rotor 21 is fixed firmly to the main shaft 34. A motor stator 2 is fixed to the body shell 1 in a manner to confront an outer periphery of the motor rotor 21. A bearing bracket 400 retaining an auxiliary bearing 42 is secured to the body shell 1 in a lower part of the hermetically sealed enclosure, for journally supporting a distal end of the main shaft. In addition, a lubricant pump mechanism 601 is arranged under the bearing bracket 400. The pump mechanism 601 supplies lubricant collected in a bottom space of the hermetically sealed enclosure to the compression mechanism through a lubricant passage provided in an inside of the main shaft 34.
A method of assembling the above-said hermetic motor compressor of the prior art will now be described hereafter.
First, the body shell 1 is heated to expand thermally, and shrinkage fit the motor stator 2 in it. Next, the bearing bracket 400 is positioned to be in parallel with the motor stator, and three-point spot welding is made with its peripheral rim held in contact to the body shell 1. Then, the compression mechanism 300 is inserted so that the distal end of the main shaft is journally supported by the bearing bracket 400 via the auxiliary bearing 42. There is arranged in this connection that a gap of approximately 0.25 mm is provided between an outer diameter of the compression mechanism 300 and an inner diameter of the body shell 1, so as to absorb a play in the bearing. Next, the compression mechanism 300 and the body shell 1 are fixed by three-point spot welding, after the compression mechanism 300 is adjusted within a margin of this gap so that a center of it is in alignment with a center of the auxiliary bearing 42. The reason for providing the gap between the compression mechanism and the body shell for absorbing the play in the bearing is that a satisfactory mechanical strength is not otherwise obtainable when two plate-like metals such as the auxiliary bearing bracket and the body shell are spot-welded together while a gap remained existent between them.
However, the above structure and the assembling method of the prior art have such problems as stated hereinafter.
(1) The compression mechanism shifts in a direction toward a point that begins to melt first among the three points when the three-point spot welding is being made on the compression mechanism.
(2) The bearing bracket deforms, although only slightly, when it is used as a positioning reference since it is fabricated normally by sheet metal stamping. This makes it difficult to carry out the positioning accurately.
(3) The compression mechanism shifts in its position due to a stress it receives when the upper shell is press-fit, since the compression mechanism is fixed to the body shell only by the spot welding at three points.
If the individual components are assembled improperly in their positions with respect to each other as described above, the hermetic motor compressor causes excess vibration, bearing losses, and wear in the sliding parts. Consequently, they bring rise to problems affecting the quietness, efficiency, reliability, and so forth.
The present invention is devised in consideration of the above problems of the prior art. A hermetic motor compressor of this invention comprises:
(1) a main shaft constructed at one end of a crankshaft for rotatory driving a orbiting scroll member which is in engagement with a stationary scroll member to form a plurality of compression spaces;
(2) a compression mechanism having a main bearing supporting the main shaft in a freely rotatable manner;
(3) a motor comprising a rotor fixed to the main shaft, and a stator having a stator winding wound on an iron core with an electrical insulator;
(4) an auxiliary bearing journally supporting a distal end of the main shaft;
(5) a bearing holder retaining the auxiliary bearing;
(6) a bearing bracket mounting the bearing holder in any of a slidable manner and a stationary manner;
(7) an auxiliary bearing assembly positioned at one side of the motor opposite the compression mechanism;
(8) a cylindrically-formed body shell which retains and encloses the compression mechanism, the motor and the auxiliary bearing assembly, and that
the stator of the motor is fixed into the body shell by shrinkage fit, and the compression mechanism is welded after it is shrinkage-fit into the body shell.
Further, a method of assembling the hermetic motor compressor of this invention comprises:
(1) a first step for shrinkage-fitting the stator of the motor into the body shell;
(2) a second step for shrinkage-fitting the compression mechanism to the body shell followed thereafter by welding;
(3) a third step for fixing the bearing bracket integrally to the body shell; and
(4) a fourth step for shifting the bearing holder and the bearing bracket slidingly in a radial direction while turning the main shaft with an external force and measuring a turning torque of it, and for fixing the bearing holder to the bearing bracket at a position where the rotating torque becomes smallest.